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Guofan Jin

Publications and source records attributed to Guofan Jin.

14 recordsLinked to original sources
PubMed2006

Design and experimental test of diffractive superresolution elements.

By using previously established methods based on linear programming (MLP), we design and fabricate two types of diffractive superresolution element (DSE). The structure parameters and superresolution performances of the fabricated DSEs are tested. The test results agree well with the design results and are applicable to a writable or a read-only optical disk. Thus the application validity of the MLP is experimentally verified.

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PubMed2005

Improvement to human-face recognition in a volume holographic correlator by use of speckle modulation.

We show that a speckle-modulation technique can improve the parallelism and the recognition accuracy of volume holographic correlators. The object patterns are modulated by a speckle pattern generated by a diffuser. These modulated patterns are stored as Fourier holograms by use of angular-fractal multiplexing. With the speckle modulation the sidelobes are completely suppressed, the cross talk is negligible, and the correlation peak becomes a bright sharp spot. Thus higher recognition accuracy is achieved. The angular separation between adjacent patterns in the multiplexing could be much smaller, resulting in larger capacity and higher parallelism of the correlator. Also, this technique can be combined with other methods such as wavelet filtering to achieve a large invariant tolerance range. Theoretical analysis, numerical evaluation, and experimental results are presented to confirm that sidelobes and cross talk are sharply suppressed by the speckle modulation.

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PubMed2005

Compact optical roll-angle sensor with large measurement range and high sensitivity.

A simple and effective optical roll-angle sensor based on a magnetic garnet single crystal is demonstrated. The measurement is based on the principle that, when linearly polarized light whose polarization varies alternately in two orthogonal directions passes through a polarization analyzer, the transmitted optical intensity varies. The output voltage from an optical detector located after the analyzer can be used to determine the roll angle. The chief advantages of the sensor are that it is compact, flexible, low cost, and power effective and provides a fast response. Most importantly, the sensor is insensitive to various fluctuations such as optical intensity, photodiode responsivity, and temperature and to vibrations. This performance is most advantageous in long-distance or long-term measurements. Experimental results have shown that the angular resolution is 0.01 degree in a +/-30 degree range.

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PubMed2005

Design theories and performance limits of diffractive superresolution elements with the highest sidelobe suppressed.

For the application of optical data storage, theories that we present can be used to design a diffractive super-resolution element (DSE) with the highest sidelobe suppressed. A globally optimal solution among general hybrid-type filters can be solved through linear programming. The obtained globally optimal performances set the exact performance limits of a general hybrid-type DSE with the highest sidelobe suppressed. A comparison of our design theories and the previous design methods shows the advantages of the former.

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PubMed2004

Design and fabrication of continuous-profile diffractive micro-optical elements as a beam splitter.

An optimization algorithm that combines a rigorous electromagnetic computation model with an effective iterative method is utilized to design diffractive micro-optical elements that exhibit fast convergence and better design quality. The design example is a two-dimensional 1-to-2 beam splitter that can symmetrically generate two focal lines separated by 80 microm at the observation plane with a small angle separation of +/- 16 degrees. Experimental results are presented for an element with continuous profiles fabricated into a monocrystalline silicon substrate that has a width of 160 microm and a focal length of 140 microm at a free-space wavelength of 10.6 microm.

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PubMed2004

Comparison of defocusing and fractional Fourier transform in spectroholographic storage.

In spectroholographic storage systems the defocusing method is often used for spectrum uniformity and quality improvement of recorded information. The same purpose is served by the fractional Fourier transform (FRFT) storage system. To simplify the numerical analysis, we derive the expressions of the Fraunhofer spectrum and the reconstructed image at the detected plane (CCD) for both cases instead of using the Fresnel spectrum and the FRFT spectrum. The recording aperture, spectrum uniformity, and reconstructed information of both systems are investigated. A numerical comparison is also presented.

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PubMed2004

Broadband polarizing beam splitter based on the form birefringence of a subwavelength grating in the quasi-static domain.

We propose a novel broadband polarizing beam splitter with a compact sandwich structure that has a subwavelength grating in the quasi-static domain as the filling. The design is based on effective-medium theory an anisotropic thin-film theory, and the performance is investigated with rigorous coupled-wave theory. The design results show that the structure can provide a high polarization extinction ratio in a broad spectral range.

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PubMed2004

Improved fast fractional-Fourier-transform algorithm.

Through the optimization of the main interval of the fractional order, an improved fast algorithm for numerical calculation of the fractional Fourier transforms is proposed. With this improved algorithm, the fractional Fourier transforms of a rectangular function and a Gaussian function are calculated. Its calculation errors are compared with those calculated with the previously published algorithm, and the results show that the calculation accuracy of the improved algorithm is much higher.

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PubMed2003

Analysis of power-dependent phase-matched four-wave mixing in dispersion-managed transmission systems.

We investigate power-dependent phase-matched four-wave mixing (FWM) in wavelength division multiplexing transmission lines, in which positive and negative dispersion fibers are alternately arranged to manage the dispersion and the dispersion slope. The FWM effect shows power-independent phase matching when the channel power is low. However, it is power dependent at high power. The maximum FWM conversion efficiency is shifted away from the zero channel space in the case of power-dependent phase matching. Optimization of the dispersion system for suppression of the FWM effect is determined.

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PubMed2003

Design of three-dimensional superresolution filters and limits of axial optical superresolution.

Theories to design a three-dimensional superresolution filter (TDSF) for confocal microscopy are proposed that can obtain a globally optimal solution through linear programming. The designed TDSF is proved to be a phase-only element introducing a phase delay of 0 or pi. Five design examples of the TDSF are presented to demonstrate the validity of these theories, Regardless of transverse superresolution, a curve of Seu(Ga+/-) defined as the maximum value of Strehl ratio S under the axial resolving power of Ga+/- is calculated to set the fundamental limits of axial optical superresolution. Finally, what is to our knowledge a novel analytic expression of Seu(Ga+/-) is deduced.

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PubMed2003

Theories for the design of a hybrid refractive-diffractive superresolution lens with high numerical aperture.

By geometrical optics and the Rayleigh-Sommerfeld diffraction formula, theories for the design of a hybrid refractive-diffractive superresolution lens (HRDSL) with high numerical aperture are constructed. Differences between the profile of the diffractive superresolution element (DSE) with high numerical aperture and that with low numerical aperture are indicated. Optimization theory can obtain a globally optimal solution through a linear programming much more simplified than the corresponding one in Liu et al. [J. Opt. Soc. Am. A 19, 2185 (2002)]. The rules of the structure of the designed DSE are both theoretically proved and numerically verified. Comparison of this optimization theory with the other design theories and examples of designing the HRDSL with high numerical aperture are provided. Last, some limits of optical superresolution with high numerical aperture are set and compared with those for low numerical aperture.

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PubMed2002

Suppression of the influence of a photovoltaic dc field on volume holograms in Fe:LiNbO3.

A nonuniform photovoltaic field is created in Fe:LiNbO3 during hologram recording exposures. Experimental results and analysis show the degradation of the volume holograms in the presence of the photovoltaic field. A sodium chloride solution is used to short-circuit the crystal to improve the stored-image quality. Experimental results to demonstrate the effectiveness of the proposed method are presented.

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PubMed2002

Theories for the design of diffractive superresolution elements and limits of optical superresolution.

We suggest using the theory of linear programming to design diffractive superresolution elements if the upper bound of the intensity distribution on the input plane is restricted, and using variation theory of functional or wide-sense eigenvalue theory of matrix if the upper bound of the radiation flux through the input plane is restricted. Globally optimal solutions can be obtained by each of these theories. Several rules of the structure and the superresolution performance of diffractive superresolution elements are provided, which verify the validity of these theories and set some limits of optical superresolution.

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